Ceramic compositions employing a substantial amount of alumina (Al.sub.2 O.sub.3) as a base material are known in the art. Alumina based compositions are advantageous for the production of cutting tools due to their high temperature resistance and wear resistance.
However, such compositions suffer from significant brittleness. Accordingly, much attention has been directed to combining various additives with alumina to improve the hardness and strength of the ceramic composition.
For example, U.S. Pat. No. 4,218,253 discloses the addition of tetragonal zirconium oxide to the aluminum oxide base material to improve toughness.
More recently, U.S. Pat. No. 4,452,906 discloses ceramic compositions of alumina comprised of an essentially homogenous admixture of alumina with certain other refractories including zirconia and tungsten carbide to improve hardness and strength. The '906 patent indicates that in many instances improvement in properties of ceramic compositions containing additives such as zirconia are accompanied by the impairment of other properties.
Accordingly, considerable attention has been focused on maximizing the properties of hardness and toughness of alumina based ceramics. One such approach has been to incorporate into alumina based compositions, silicon carbide whiskers as a reinforcing agent.
U.S. Pat. No. 4,543,345 discloses ceramic composites strengthened with silicon carbide whiskers having a monocrystalline or single crystal structure in an amount of 5 to 60 volume percent. The single crystal SiC whiskers are stated to improve fracture toughness by their ability to absorb cracking energy. Ceramic materials which are stated to exhibit improved hardness in this manner include alumina, mullite (3Al.sub.2 O.sub.3.2SiO.sub.2) and B.sub.4 C as well as cordierite (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.3).
On the other hand, the '345 patent indicates that the use of silicon carbide whiskers does not improve the toughness of certain ceramic materials including ceramic materials containing both alumina and zirconia.
Applicants have sought to develop a ceramic composite material which is based on alumina having improved toughness and hardness. To this end, applicants have discovered that the addition of specific amounts of particulate zirconia to an alumina based ceramic along with the incorporation of SiC carbide whiskers in specific amounts results in a ceramic composite which surprisingly exhibits the properties of both excellent hardness and toughness which is superior to ceramics known in the art.
It is therefore an object of the invention to provide a ceramic composite which exhibits excellent wear resistance, fracture toughness and hardness.
It is another object of the invention to provide a method of making a ceramic composition containing alumina, zirconia and reinforced with silicon carbide whiskers.